1. Field of the Invention
The present invention relates in general to computer disk storage management and more particularly to a no-integrity management method and system for a logical volume of a computer system.
2. Related Art
Direct access storage devices (DASD) are widely used in mainframe computer systems to store data. In order to manage these direct access storage devices, several disk management techniques are available. One useful and popular technique is logical volume management. Instead of interfacing directly with a physical partition on the direct access storage device, a logical volume manager (LVM) divides the disk space on the drive into logical partitions. A logical partition may include several direct access storage devices but is transparent to a user, which means that the logical partition appears to the user as a single storage device.
At the lowest level of logical volume management is the physical direct access storage device itself. Each individual direct access storage device is formatted into a physical volume (PV) for use by the LVM. Each physical volume has a name and belongs to a volume group (VG). A volume group is a collection of direct access storage devices under the management of the LVM that are treated as a single large storage area. All physical volumes within a volume group are divided into physical partitions (PPs) of a certain size. These physical partitions are allocatable units of disk space, typically on the order of 2 megabytes or 4 megabytes. The total number of physical partitions on each direct access storage device varies and depends on the total capacity of the direct access storage device.
Each volume group defines one or more logical volumes (LVs). Logical volumes are groups of information located on physical volumes. Although data on a physical volume can be discontinuous, the data on a logical volume appears to the user as contiguous. This arrangement permits file systems, paging space and other logical volumes to be resized or relocated, span multiple physical volumes and have their contents replicated for greater flexibility and availability in data storage. Each logical volume includes one or more logical partitions (LPs), with each logical partition corresponding to at least one physical partition.
Mirroring of a logical volume is a technique that provides copies of the logical volume and prevents data loss due to disk failures, thereby offering greater data reliability. If mirroring is specified for a logical volume, the LVM allocates additional physical partitions to store the additional copies of each logical partition. Although the logical partitions are numbered consecutively, the underlying physical partitions are not necessarily consecutive or contiguous. The LVM marks each partition of the mirrored copies of the logical volume with an availability status that can be either stale or active. Only partitions that are marked as active can be read and written.
In general, the LVM changes the availability status of a partition from stale to active by using a swap space (also called a paging space). The swap space allows information to be swapped between random access memory (RAM) and the direct access storage device. By way of example, to change the availability status of a partition from stale to active the LVM uses the swap space to copy information from an active mirrored partition to a stale mirrored partition. The LVM keeps track of the availability status of each partition by writing the availability status information to the direct access storage device. Thus, at any point in time the availability status of each partition is stored in the direct access storage device and retained even if the computer system is shutdown. When the computer system is restarted, the availability status of each partition read from the direct access storage device and each partition is marked as either stale or active.
One problem with this type of logical volume management is that keeping track of the availability status of each partition on the direct access storage device uses a great deal of computer system resources. In particular, resources must be used to continually write and store partition availability status to the direct access storage device. Storing the availability status of each partition to the direct access storage device, remembering the status after system shutdown and marking each partition""s availability status after system restart utilizes a tremendous amount of computer system resources and overhead. This overhead decreases performance of the computer system because the processor is busy writing and reading to the swap spaces and direct access storage device instead of processing other requests.
Accordingly, what is needed is a method for managing logical volumes (especially mirrored logical volumes) that does not keep track of the availability status of each logical volume partition on the direct access storage device. Instead, what is needed is a method that keeps track of the availability status in such a way that computer system resources are not heavily taxed. What is further needed is a method of logical volume management that saves computer system resources by not having to mark the availability status of each partition as either stale or active upon restart of the computer system.
To overcome the limitations in the prior art as described above and other limitations that will become apparent upon reading and understanding the present specification, the present invention includes a no-integrity management method and system for managing logical volumes of a computer system. The no-integrity management of the present invention keeps track of an availability status of each logical volume partition in volatile memory, such that the information is lost after computer system shutdown. Moreover, upon computer system restart the availability status of each partition is set to active.
The present invention conserves valuable computer system resources by eliminating the need to read and write availability status information to a direct access storage device. By keeping track of availability status information and any changes to that information in volatile memory, the present invention reduces overhead and permits system resources to be used for other tasks, thereby increasing system performance. Moreover, the present invention does not retain prior availability status information after system shutdown, thereby eliminating the need and overhead involved in storing and redesignating the availability status for each partition.
Other aspects and advantages of the present invention as well as a more complete understanding thereof will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. Moreover, it is intended that the scope of the invention be limited by the claims and not by the preceding summary or the following detailed description.